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## Ciencia del suelo

*versión On-line* ISSN 1850-2067

#### Resumen

PICONE, Liliana et al. Phosphorus transfomations in a mollisol under contrasting tillage practices.* Cienc. suelo* [online]. 2007, vol.25, n.2, pp. 99-107. ISSN 1850-2067.

Conservation tillage may affect soil phosphorus (P) fractions through the application of P fertilizer and the deposition of residue on the soil surface. The objectives were to 1) evaluate the effect of tillage systems on soil P fractions, as well as the interaction with P fertilization, and 2) relate changes in P fractions with P balance. No tillage and conventional tillage were assigned as main plots and the two P rates (0 y 30 kg P ha^{-1}) the subplots, with three replicates. Inorganic (Pi) and organic (Po) P were measure with the anion exchange membrane (AEM), NaHCO_{3}, NaOH, HCl and residual fractions, extracted sequentially. When the amount of P applied exceeded that removed by grain, the P excess was converted to different fractions, but with no increases in Bray-P compared to initial value. In the short time, there was no interaction neither significant effect of tillage systems on Pi forms; however, the AEM-Pi and NaHCO_{3}-Pi fractions were significantly (p< 0,05) higher with P application. Without consideration of residual-P and among the inorganic forms, the HCl-Pi showed high values, in absolute (50 mg P kg^{-1}) and relative (9% of total P) terms, according to geochemical characteristics of these soils. There was no interaction of fertilizer application with tillage neither main effects on Po fractions. Among all P fractions, NaOH-Po was the most abundant (186,7 mg P kg^{-1} and 34% of total P), followed by residual-P. In agreement with the positive P balance, total P tended to be higher with P application and the sum of fractions extracted by AEM, NaHCO_{3}, NaOH y HCl accounted, on average, for 81% of the increment in total P.

**Palabras clave
:
**Sequential phosphorus fractionation; Phosphorus balance; No tillage; Conventional tillage.